The present application relates generally to hydraulic systems. The present application relates more specifically to controlling the pressure rise rate in a hydraulic lift and flotation system.
Harvesting machines can use hydraulic lift and flotation systems to permit their headers to ride lightly up and over rises in the terrain during field operation. Hydraulic lift and flotation systems can include a pump, relief valve and unloading valve to supply and regulate hydraulic fluid flow. The unloading valve is a solenoid operated single direction check valve that is closed to block the oil flow path from the pump in order to build pressure in the system before forcing the oil through the relief valve. The pressure between the unloading valve and the relief valve is the system pressure used for the lift and flotation functions.
In current hydraulic lift and flotation systems, a fixed voltage signal is used to close the unloading valve. Depending on the normal state of the unloading valve, the voltage signal is either applied or removed to close the unloading valve. The unloading valve can close rapidly, which results in the pressure at the pump rising to to a magnitude greater than the relief pressure (the pressure necessary to open the relief valve) in a very short amount of time. The relief valve has a response rate that is incapable of reacting quickly enough to absolutely clamp pressure at its relief setting. The rapid uncontrolled/unregulated rise in pressure can cause damage to the pump and reduce the life of the valves, e.g., the relief valve, the unloading valve, and other components in the system.
Therefore, what is needed is a control system that can regulate the rate of pressure rise or increase in a hydraulic lift and flotation system to avoid damage to the system components.